How Can Journal Impact Factors Be Normalized Across Fields of Science? An Assessment in Terms of Percentile Ranks and Fractional Counts

effects of (a) fractional counting on the impact factor (IF) and (b) transformation of the skewed citation distribu-tions into a distribution of 100 percentiles and six per-centile rank classes (top-1%, top-5%, etc.). Do these approaches lead to field-normalized impact measures for journals? In addition to the 2-year IF (IF2), we con-sider the 5-year IF (IF5), the respective numerators of these IFs, and the number of Total Cites, counted both as integers and fractionally. These various indicators are tested against the hypothesis that the classification of journals into 11 broad fields by PatentBoard/NSF (National Science Foundation) provides statistically sig-nificant between-field effects. Using fractional counting the between-field variance is reduced by 91.7 % in the case of IF5, and by 79.2 % in the case of IF2. However, the differences in citation counts are not significantly affected by fractional counting. These results accord with previous studies, but the longer citation window of a fractionally counted IF5 can lead to significant improvement in the normalization across fields